1. Field of the Invention
The subject invention generally relates to hydrometers and, more specifically, hydrometers suited for continuous use in automotive applications.
2. Description of the Prior Art
Hydrometers have been used for many years to test the freezing points of coolant liquids in motor vehicles. Typically, these hydrometers have utilized float tubes with appropriate internal scales that provide a reading of the freezing point based upon the specific gravity of the coolant fluid. Examples are described in U.S. Pat. Nos. 1,578,193; 1,817,676; 1,890,900; and 2,002,183. Such hydrometers provide an accurate reading, but are relatively delicate and costly to construct and maintain.
Ball-type hydrometers have been developed for medical and other applications which are less precise, but more durable and less expensive. These hydrometers use balls of different specific gravity to continuously measure the specific gravity of the fluid. When a ball of a known specific gravity floats at the surface of the liquid, it is known that the specific gravity of the fluid is greater than the ball. By identifying which balls float on the surface of the liquid, the specific gravity of the liquid can be identified within a given range. Examples are shown in U.S. Pat. Nos. 1,556,185; 3,626,763; and 3,631,727.
In some of these systems, such as shown in U.S. Pat. No. 3,631,727, the balls are maintained in separate compartments to aid in identifying which balls are floating. However, such hydrometers were generally not well-suited for use in motor vehicles. The coolant fluids in motor vehicles generally contain relatively high quantities of impurities, because motor vehicle coolant systems are generally exposed to high levels of rust and dirt.
Accordingly, there was a need in the prior art for a simple, inexpensive hydrometer that was adapted for use on motor vehicles and that would quickly and reliably monitor specific gravity of a coolant fluid.